Airplanes are traditionally constructed using mostly aluminum and steel, with composite materials limited to smaller portions of their structure. Boeing, however, opted to increase the use of composite materials, eliminating 1,500 aluminum sheets and 40,000-50,000 fasteners -- just from the fuselage of the plane alone [source: Boeing].
Composites are materials that are made up of more than one element. For instance, a piñata is made from a composite of paper and paste. The Dreamliner uses composites that are called carbon reinforced plastics (CRFPs). You can think of those carbon fibers as the "paper," and those fibers are embedded in a plastic matrix ("paste"), such as an epoxy resin.
Manufacturing carbon composites is much more complicated than dipping paper in paste, but it follows the same general principle. The process begins by generating carbon fibers made from another polymer, called polyacrylonitrile (PAN). Processing PAN in a series of complicated heating and stretching steps purifies the carbon atoms, which rearrange themselves from ladder to ringlike structures and take the form of long sheets of ribbon. Packing the ribbons together creates carbon fibers. Following further processing, the fibers are used to reinforce a plastic matrix, which is in a thick, gooey state. The resulting composite can then be molded before another heating process hardens it into an ultrastrong material. In fact, CRFPs are so strong that, at one-quarter the density of steel, they are two to three times stronger than steel [source: Flight International]. Not only that, they're superlight as compared to metal.
CRFPs have been around for more than 40 years. They have been used extensively to replace aluminum or steel in golf shafts, fishing rods, medical equipment and machine parts, or to repair bridges. Even some racing bicycles are made from CRFPs.
The use of composites in the Dreamliner isn't groundbreaking, but the extent to which they are used is. As much as 50 percent of the plane is composite material by weight, compared to, say, 12 percent in the Boeing 777 [source: Boeing]. In fact, the Dreamliner is the first aircraft in which the wing and fuselage are constructed from composite materials. And, as we'll see next, manufacturing a one-piece fuselage section out of composites isn't a piece of cake; however, by replacing so much metal with composites, the plane is not only much lighter but is also more aerodynamic. Features, such as sweptback wings, which aren't possible with metal, could be engineered into the plane because of the increased malleability of composites.
What's more, composites corrode less and are more robust than metal, which reduces the maintenance required for the plane. Composites have lower thermal and electrical conductivity than metals, however. This meant that Boeing had to develop entirely different approaches for managing the electrical and thermal systems on the plane to deal with shorts and the like.
An added benefit of a stronger composite fuselage structure is that higher pressurization in the passenger cabin is possible. This makes humidity, ventilation and temperature easier to control. We'll see how Boeing exploited this feature when designing the interior for the Dreamliner later, but first let's look at what the aviation industry considers Boeing's most revolutionary feat -- building the plane.